Add ESLint 6 support

[mrmckeb]

Closes #7268.

[mrmckeb]

Hi @not-an-aardvark,

I saw that you've worked a lot on the ESLint 6 resolution changes. Our config has broken as we've upgraded to ESLint 6 and I'm not sure how to resolve it - any help would be greatly appreciated!

[not-an-aardvark]

It looks like the issue is that eslint-plugin-import fails to be loaded. I think the solution would be to use the --resolve-plugins-relative-to flag (which is intended for projects like create-react-app that install plugins and run ESLint on behalf of the end user).

I think adding a property like resolvePluginsRelativeTo: __dirname here should fix the issue.

[mrmckeb]

Thanks @not-an-aardvark, that was spot-on. Does this change mean that we could make the plugins dependencies of the shared config now, as opposed to peer dependencies?

Again, thanks for your help on this!

[not-an-aardvark]

No, they still have to be peer dependencies at this point. If you're interested, eslint/rfcs#14 contains some additional info/discussion on the possibility of allowing them to be dependencies in the future.

[mrmckeb]

Thanks @not-an-aardvark - will check that out and follow it!

And thanks for the approval @ianschmitz.

[Timer]

Docs need updated to reflect new versions.

[mrmckeb]

Good pick-up @Timer! Will do in the next few hours.

[nickmccurdy]

Thanks for supporting this. Is there a timeline for the next eslint-config-react-app release?

[mrmckeb]

Yes, 100%. We had planned it for this week, but I think it's likely to be next week.

Very close now :)